Much of what we know could only have been learned from other people. For children to be able to take advantage of their culture's accumulated knowledge and expertise, they must be receptive to what people tell them, sometimes even when that information conflicts with their own expectations. And yet, children should not be entirely credulous: Due to error, ignorance, or deception, people sometimes say things that are false. The purpose this application, which is part of a larger program of research on how children make use of different sources of information to learn about the world, is to examine very young children's willingness to revise an erroneous belief about a physical event on the basis of what someone tells them. The specific aims of this application are (1) to determine the circumstances under which testimony can influence children's mistaken beliefs about the physical world, and (2) to compare children's willingness to revise their beliefs after hearing about an unexpected physical event with their willingness to do so after witnessing it themselves. In the six proposed studies, an experimenter will contradict a robust (but erroneous) belief young children hold about falling objects-namely, that they fall straight down even when their path is actually determined by a crooked tube or by forward momentum. Under a variety of conditions, children between 23 and 37 months of age will be asked to make a prediction about the trajectory of a ball before they hear about or see an event and again after, and their responses compared. The "testimony" of others is a vital (and uniquely human) method of knowledge acquisition. The proposed research is important because it will expand our knowledge of how cognitive, linguistic, and social processes interact to support learning. It also has important public health implications in terms of how parents, caregivers, and educators can craft their messages to children to effect changes in behaviors and beliefs. [unreadable] [unreadable] [unreadable] [unreadable]